1. Field of the Invention
This invention relates to an ultraviolet-transmitting glass window assembly, and the method for its manufacture; and further relates programmable read only memory device which is sealed with an ultraviolet-transmitting glass window assembly and the method of making this device.
2. Description of the Prior Art
The "read only memory device" (ROM) has found wide acceptance in the electronic data processing industry. The programmable variation of this device (PROM) has also proved useful in many applications. It has recently been discovered that the program information stored in a PROM can be erased by exposing the memory chip to ultraviolet light. This erasure does not harm the chip and the erased PROM can be reprogrammed in the same manner as it was programmed originally. In order to facilitate the erasing procedure, industry has turned to a PROM package with a ultraviolet-transmitting cover. The ultraviolet-transmitting covers commonly used in the art are made from quartz or artifical quartz (fused silica). The quartz PROM covers of the prior art have a number of drawbacks. Because quartz has such a high melting point, the forming of PROM covers from this relatively cheap raw material is very expensive. The quartz covers also require time consuming and expensive finishing steps such as mechanical machining and lapping them into shape. In addition, there does not appear to be any way to make a reliable hermetic seal with quartz at a reasonable cost.
Quartz covers are currently sealed onto the PROM package in two ways. The first method is to affix the quartz cover to the package with epoxy. This method has proven unsatisfactory for most applications since moisture can migrate through the epoxy seal and damage the sensitive memory chip. Additionally, since epoxy will not generally provide good adherence between smooth surfaces, it is often necessary to abraid or etch the edge of the quartz. This abrasion creates additional channels for the transmission of moisture through the epoxy seal. The second method now employed to seal quartz covers to PROM packages is to metalize a ring around the edge of the quartz and then solder the metalized surface to the package. One disadvantage to this method is that metalizing the quartz is a very expensive procedure. Metalization is also a sophisticated and tricky process which may produce defects in the metalized seal.